Solar Energy 101

CellA solar cell is the basic component of solar modules. Cells are manufactured from wafers. Learn how a solar cell works

CO2An abbreviation for carbon dioxide. CO2 is well-known as a “green-house gas.” When people talk about “Carbon Footprint,” they are usually referring to CO2 emissions.

Conversion efficiencyThis measure gauges the percentage of solar (light) power reaching a module that is converted into electrical power. Conventional cells now range in the high percentage teens. Theoretical and laboratory conversion rates typically are much higher than rates from mass production.

CrystalA crystal is a solid with molecular building blocks, such as atoms or ions, that have arranged themselves in an identically repeating pattern along all three spatial dimensions.

Energy PaybackThe amount of time required for a solar panel to generate the amount of energy it took to manufacture it. Modern PV panels have an energy payback of 1 to 3 years depending on where they’re installed; over a 30+ year life, a PV system will return 10 to 30 times the energy that went into making them.

Grid ConnectedA grid-connected solar electric system generates its own electricity and feeds its excess power into the utility grid for later use. Grid-connected solar electric systems are eligible for many incentives and rebates.

InverterThe inverter electronically converts Direct Current (DC) power into Alternating Current (AC) power and is required for grid-connected solar power systems.

Micro inverters can be installed on each solar module. The cost is typically higher, but they provide certain advantages for very small or geometrically complex PV systems.

String inverters are the most common type of inverter for residential and small commercial PV systems.

Central inverters are used for very large PV systems.

InsolationSunlight varies by region. Insolation is a measure of the solar radiation energy in a given region. It is usually expressed as the intensity of light energy per unit of land area. As a whole, the U.S., especially the sunny Southwest and Southeast, offers strong insolation. By comparison, Germany, the PV industry’s leader, gets little better sun than Alaska.

kWhThe abbreviation for kilowatt-hours, a unit of energy. One kWh represents a 1,000 watt load operated over a period of one hour—that's the amount of energy an average plasma TV uses. Electricity rates are most commonly expressed in cents per kilowatt hour.

MicronIn cell production, manufacturing steps occur in dimensions measured in microns. In the metric system, a micron is one millionth of a meter, or one thousandth of a millimeter. For reference, a human hair measures about 100 microns across.

Million Solar Roofs InitiativeThis is a state of California initiative to facilitate the installation of solar energy systems on one million US buildings by 2010. This initiative is largely responsible for the rebates and incentives available in California and serves as a model for many other state solar programs.

ModuleCommonly called a “solar panel,” a PV module is composed of multiple solar cells that are electrically connected to increase the total power output and are encapsulated in tempered glass for weather protection and ease of handling.

MonocrystallineSilicon is a metal and, therefore, its atoms are organized into a crystalline structure. Monocrystalline refers to silicon that is pulled as a single, completely homogenous crystal, as SolarWorld does in the USA. Monocrystalline PV cells are generally the most efficient and reliable available.

MWThe abbreviation for megawatt, a unit of power or capacity of a generator. 1 MW = 1,000 kW = 1,000,000 W.

Net-MeteringNet-metering allows the solar electric system to send excess electricity back through the electric meter to the utility. The meter actually runs backwards! Your utility will bill you for the net (kWh used – kWh generated). While most utilities will not pay you cash if you generate more than you use, many will carry forward a credit toward your next bill.

PhotonA photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. Solar radiation arrives on the surface of photovoltaic cells in the form of photons, providing the main energy that activates cells to produce electricity.

PolycrystallineOfficially called “multicrystalline,” this refers to cast silicon where several crystals form in a mold. SolarWorld’s German factories use this casting process as it is less expensive than pulling single crystals, but the resulting cells generally have lower efficiency due to internal resistance along the grain boundaries. Polycrystalline cells can be recognized by a visible grain, a “metal flake effect.”

SiliconThe basic material used to make solar cells. It is the second most abundant element in the earth’s crust, after oxygen.

Silicon carbideSilicon carbide (SiC), silicon bonded with carbon, is another member of the silicon family of materials used in the PV industry. It is a common abrasive in many industries, used in everything from grinding to sandblasting. At SolarWorld, crushed SiC is mixed into a water slurry and applied to saw wires. Silicon carbide, not wire, actually does the cutting.

Stand-alone systemEnergy generated by these systems is stored in batteries and then subsequently used. Also known as “off-grid,” these systems are not connected to the utility grid.

WaferA sawn silicon disc, used as the starting point for manufacturing a solar cell.